Many business activities involve a fleet of vehicles or other movable assets traveling to a number of destinations under the management of a central headquarters or base station. Examples include fleets of delivery trucks and railroad trains. Management and dispatching personnel at the base station generally desire the capability to monitor the itinerary actually traveled by each mobile unit. Such monitoring capability would permit managers and dispatchers to confirm whether the mobile unit deviated from a prescribed itinerary, or whether the driver violated regulations regarding speed limits or required periods of rest.
Various systems have been used to monitor fleets of mobile units by means of the U.S. Government operated G.P.S., Navstar, Argos, and Loran satellite navigation systems. Examples are described in U.S. Pat. No. 5,119,102 issued Jun. 2, 1992 to Barnard; and U.S. Pat. No. 5,223,844 issued Jun. 29, 1993 to Mansell et al.
However, conventional systems by which a base station monitors the itineraries of one or more mobile units generally require the mobile units to remain in continuous or frequent radio communication with the base station. Such systems cannot monitor the itinerary of a mobile unit which travels out of communication range of the base station. Even systems which communicate via public cellular telephone networks cannot function when a mobile unit travels to a rural location lacking cellular telephone service.
Therefore, a need exists for a system which monitors the itinerary of a mobile unit even when the mobile unit does not communicate with the base station during all or a portion of its travels.
A similar need exists for tracking stolen goods by law enforcement personnel. As described in U.S. Pat. No. 4,908,629 issued Mar. 13, 1990 to Apsell et al., systems have been developed for locating a stolen automobile in which a police transmitter commands a transceiver hidden in the stolen automobile to begin transmitting a radio beacon so that it can be located using direction finding receivers. However, it would be desirable if the stolen automobile could transmit its geographical coordinates instead of a mere beacon. It would be even more desirable if the stolen automobile could store a history of all locations it has traversed (i.e., its itinerary) to help the police find the thieves and their accomplices. The same need exists for tracking any other type of valuable, movable asset.